Electrophotographic reproduction material

ABSTRACT

Photoconductive compositions containing a resin and as a photoconductor, a 2-tricyanovinyl-pyrrol, a 3-tricyanovinylindole or a tricyano-vinyl-benzene which may have an amino or hydroxy group in 4-position, optionally including an optical sensitizer, and electrophotographic reproduction materials having a layer of said composition adhering to a substrate.

United States Patent [1 1 Tellier et al.

[ 1March 20, 1973 ELECTROPHOTOGRAPHIC REPRODUCTION MATERIAL [75] Inventors: Jacques C. T. Tellier, Conklin, N.Y.;

Henri G. J. deBoer, Delft, Netherlands [73] Assignee: GAF Corporation, New York. NY.

22 Filed: July 22, 1971 [21] Appl. No.: 165,408

Related u.s. Application Data [63] Continuation of Ser. No. 723,590, April 23, 1968,

4/1966 Sus et al. ..96/1

8/l966 Kosche .96l l.l 4/ i966 Tomanek et al ..96/ 1 Primary Examiner-George F. Lesmes Assistant Examiner--M. B. Wittenberg Attorney-George L. Jane, Samson B. Leavitt, Homer J. Bridges, Martin A. Levitin, Robert H. Zappert and Walter C. Kehm [5 7 ABSTRACT Photoconductive compositions containing a resin and as a photoconductor, a Z-tricyanovinyl-pyrrol, a 3- tricyanovinylindole or a tricyano-vinyl-benzene which may have an amino or hydroxy-group in 4-position, optionally including an optical sensitizer, and electrophotographic reproduction materials having a layer of said composition adhering to a substrate.

15 Claims, No Drawings ELECTROPHOTOGRAPHIC REPRODUCTION MATERIAL This application is a continuation of Ser. No. 723,590, filed Apr. 23, 1968, now abandoned.

This invention relates to improved materials for use in electrophotographic processes.

Among the modern methods of copying, the electrophotographic process, also known as the xerographic or dry process, continues to increase in practical importance. This method consists in electrostatically charging a base material, having a photoconductive insulating layer adhering thereto, and thus rendering the photoconductive layer sensitive to light. When the material is exposed to a radiation image in a manner similar to that employed with ordinary silver halide photographic material, the electrostatic charging of the layer is reduced at the places where the light strikes the layer. Subsequently the invisible, latent elecsubstituted by an alkyl group having from one to five carbon atoms inclusive and in the 4 position of the nucleus relative to the tricyanovinyl radical may be substituted by a hydroxyl group or by a substituted or trostatic image so obtained can be rendered visible and fixed by various methods. 6

Electrophotographic materials normally consist of support on which there is a photoconductive coating or layer. It is known to make this layer by using, as photoconductive substance, selenium, sulphur or zinc oxide or substances such as anthracene and anthraquinone.

An electrophotographic material suitable as a reproduction material has to meet various requirements as regards applicability, reliability in use, lightsensitivity and stability.

Two of these properties are as follows I. The ability of the coating to hold an applied electrostatic charge in the dark.

2. The relative efficiency with which radiant energy absorbed by the photoconductive material discharges the coating.

These properties determine the utility of the coating. The first property determines whether or not the coating is useful for xerography. The coating must retain a charge long enough in the dark to permit image exposure and development.

The second property determines the photographic speed of the coating. It determines the amount of exposure to a given source of radiation necessary for image formation.

An object of the present invention is to provide a material for electrophotographic reproduction with improved properties in respect of the requirements above.

According to the present invention there is provided a material for electrophotographic reproduction comprising a substrate and a photoconductive insulating layer adhering thereto, the photoconductive insulating layer comprising a resin and a photoconductive substance consisting of at least one compound having the general formula:

where A represents a pyrrole or indole nucleus which may be substituted by an alkyl group having from one to five carbon atoms inclusive, the tricyanovinyl radical occupying position 2 of the nucleus when A is a pyrrole group and position 3 of the nucleus when A is an indole ring; or A represents a phenyl nucleus which may be unsubstituted amino group.

Thus the hydrogen atom linked to the nitrogen atom of the pyrrole or indole nucleus may be substituted by an alkyl group having from one to five carbon atoms. The alkyl group may be branched or a straight chain group and preferred examples are methyl, ethyl, npropyl, isopropyl, n-butyl', isobutyl or tertiary butyl.

When the tricyanovinyl compound is attached to a phenyl nucleus, a preferred general formula is as follows:

II II in which R and R" represent hydrogen or lower alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tertiary butyl and R is -OH or in which R, and R represent hydrogen or lower alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tertiary butyl, save that when R, represents tertiary butyl, R, is hydrogen.

Generally speaking, apart from the limitation just noted R, and R, and R and R" may be the same or different.

Thus useful compounds within the scope of the invention are B-(tricyanovinyl)-indole, 3-(tricyanovinyl)- N-ethyl-indole, 3-(tricyanovinyl)-N-methyl-indole, 3- (tricyanovinyl)-N-butyl-indole, 3-(tricyanovinyl)-N- isopropyl-indole, 2-(tricyanovinyl)-pyrrole, 2- (tricyano-vinyl)-N-ethyl pyrrole, 2-(tricyanovinyl)-N- methyl pyrrole, 2-(tricyanovinyl)-N-butyl pyrrole, 4- tricyanovinyl-2,6-dimethyl or diethyl phenol, 4- tricyanovinyl-N,N-diethyl or -dimethyl aniline, 4- tricyanovinyl-aniline, 4-tricyanovinyl-N-monomethylor N-monisopropyl-aniline, 4-tricyanovinyl-N,dipropyl aniline and 4-tricyanovinyl-2,6-diisopropyl phenol.

The structural formula of a number of compounds falling within the scope of the invention is set forth below: i

, present invention do not require the addition of sensitizers to extend their sensitivity to the visible or infrared range of the spectrum. This will be explained in more detail hereinafter.

The ratio of the tricyanovinyl compound to the resin binder may vary widely and is preferably within the range :1 to 1:10. A particularly preferred ratio is approximately 1:1.

The materials used as supp'orts may be widely varied.

Metal foils e.g. of aluminum, zinc or copper are suitable as are cellulose products such as papers or regenerated cellulose. Plastics such as polyvinyl alcohol, polyamides, polyurethanes, cellulose acetate,-

cellulose butyrate, polyesters, polycarbonates and polyolefins may be used also. Desirably the latter are covered with an electroconductive layer or converted into materials which have a specific conductivity of at least 10"" ohm cmf' e.g., by chemical treatment or by introduction of materials which render them electrically conductive. Glass plates or other insulators may also be employed. The glass may be provided with a thin conductive layer by vaporization e.g. the Nesaglass marketed by Pittsburgh Plate Glass Company.

When paper is used as the support, it is preferably pretreated against the penetration of coating solutions. Thus it may be treated with a solution of methyl cellulose or polyvinyl alcohol in water or with a solution of a copolymer or acrylic acid methyl ester and acrylonitrile, or with solution of polyamides or with dispersions of such substances. its electrical conductivity may be increased by addition of inorganic hydroscopic salts.

The resin or binder in which the tricyanovinyl compound is dispersed may be any of the known resins used for making electrophotographic materials provided that their electrical volume resistivity is higher than 10' ohm. cm. Suitable polymeric binders include silicone resins, polystyrene, styrene-butadiene polymers, polyolefins, natural resins such as balsam resins, colophony and shellac, synthetic resins such as coumarone resins and indene resins or Beckacite resins, processed natural substances such as cellulose ethers, vinyl polymers such as polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl acetal, polyvinyl ethers, polyacrylic and polymethacrylic acid esters and isobutylene or chlorinated rubber. For further discussion of suitable binders reference is made to TAPPl, October, 1966, Vol. 49, No. 10,439 and TAPPI, September 1964, Vol. 47, No. 9, 147A the disclosure of which is incorporated herein by reference.

Optical sensitizers can be included in the photoconductive coatings to increase their sensitivity in the range of visible light. Suitable chlorophyll and dyestuff compounds selected from such groups as triarylmethane dyes, rhodamines, phthaleins, cyanines, thiazines and acridines. A particularly preferred class of sensitizers are phenol sulphone phthaleins e.g. Bromophenol Blue.

A disadvantage associated with the use of sensitizers lies in the fact that many of these materials have a deleterious effect upon the insulating character of the photoconductive insulating layer. The result is that the maximum obtainable surface charge is not reached in the electrostatic charging of the photoconductive layer, and/or that the surface charge decreases too rapidly in the dark, i.e. that the material exhibits the phenomenon of a steep dark decay.

An advantage of the compounds used in the present invention is that many of them are colored and that the action spectrum coincides with the absorption spectrum, i.e., electrophotographic material containing one or more of these compounds require none, or very litsensitizers are tle, addition of sensitizers for extending the spectral sensitivity in the visible parts of the spectrum. Thus the deleterious effect of the presence of sensitizers can be avoided. Apart from this, photoconductive insulating layers, which consists wholly or partly of the materials to be used in accordance with this invention, can be sensitized very readily with known colorants, if this appears to be necessary for special reasons.

When sensitizers are used they may be employed in quantities of up to 3 percent by weight based on the weight of the photoconductive coating although small quantities of up to less than 0.01 percent by weight give effective'results.

The preparation of the photoconductive material may be carried out by methods known in the art. Thus a solution of the tricyanovinyl compound can be prepared in one or more organic solvents such as benzene, acetone, methylene dichloride, glycol monomethyl ether or dimethyl-formamide. This is then mixed with the resin and applied to the supporting matrix by painting, roller application or by spraying. It is possible for the compounds to be used in association with each other and/or other photoconductive compounds. Preferred coating weights lie between 1 and 50 gm/m, more preferably between 5 and gmslm The production of images by the electrophotographic method may take place as follows:

After charging the photoconductive insulating layers, e.g. by means of a corona discharge from charging equipment operating at 6,000.to 7,000 volts, the material is exposed underneath an original or by projection. The development of the latent picture can be achieved in a variety of ways. A very suitable method is cascade developing, wherein the developer consists of a mixture of a carrier and a toner. Glass beads, iron powder or other inorganic materials, or organic materials, for example, can be used as the carrier. The toner consists of a mixture of a fusible resin and a pigment or of a colored synthetic resin having a grain-size of l 100 p. The characteristic of the developer mixture is that, under the influence of the tribe-electrical effect, the toner particles can accept a charge of opposite sign to that of the carrier particles, the two components of the developer being so selected that the toner particles receive a charge of opposite sign to that of the electrostatic charge applied to the electrophotographic material, which charge is applied with the help of the corona discharge. The image that thus becomes visible can still be wiped off. It can be fixed by heating to about 100C. The temperature can be reduced if the action of the heat takes place in the presence of vapors from the solvents such as trichloroethylene. In this way positive images of positive originals are obtained. These electrophotographic images can be converted into an offset master after fixing if the material is washed with a solvent for the photoconductive insulating layer, e.g. ethanol or acetic acid, whereby the image-free parts of the photoconductive insulating layer are removed thus exposing the hydrophilic base material (aluminum foil), and the material is then rinsed in water and rubbed with a grease-based ink in known manner. In this way, positive offset masters are obtained, copies of which can be made in an offset machine.

The invention is illustrated by the following examples:

EXAMPLE IA One gm. 3-(tricyanovinyl)-indole and 1 gm. of a partially polymerized natural resin, e.g. the product marketed by the Hercules Powder Co. under the name Hercules Poly Pale W.G., are dissolved in 20 gm. dimethylformamide. This solution is poured on to an aluminum foil. After the solvent has evaporated, an orange photoconductive insulating layer is left, which adheres firmly to the surface of the aluminum. A negative charge is applied to the surface by means of a corona discharge, after which the layer is exposed for seconds, using a 40-Watt tungsten lamp at a distance of 1 meter. The resultant electrostatic image is rendered visible by powdering with a mixture of colorant and iron, the resin of the colorant being so selected that the colorant accepts a positive charge with respect to the iron (e.g. Hunt Toner Graph-o-fax 39-50).

A positive image appears which is fixed by warming. The aluminum foil can be converted into an offset master by removing the superfluous photoconductive material with the help of an appropriate solvent, e.g., the Entschichter 255 coating remover sold by Kalle A.G. After washing with water, the master can be fixed in an offset machine and prints can be made from it.

EXAMPLE [3 One gm. 4-tricyanovinyl-2,6-dimethyl phenol and 1 gm. of a partially polymerized natural resin, e.g. the product marketed by the Hercules Powder Co. under the name Hercules Poly Pale W.G., were dissolved in 20 gm. methylene chloride. This solution was poured out on to an aluminum foil. After the solvent had evaporated, a yellow photoconductive insulating layer was left over, which adhered firmly to the surface of the aluminum. A negative charge was applied following the procedure of Example IA and a positive image ob tained as in Example IA. The aluminum foil can likewise be converted into an offset master.

EXAMPLE "A One gm. Z-(tricyanovinyl)-N-butyl-pyrrole and 1 gm. Kunstharz A.W.2. synthetic resin, marketed by Messrs. B.A.S.F., are dissolved in 50 cm benzene. The solution is applied to paper and dried. High-contrast copies of the original are obtained direct by employing methods'normally used in electrophotography. The" photoconductive material can be used with aluminum foil as the carrier in exactly the same way as in Example I. A very good offset master is obtained after the usual treatment.

EXAMPLE "B EXAMPLE lllA Ten mg. Rhodamine-B extra (B.A.S.F.), dissolved in 10 gm. dimethyl-formamide, were added to a solution consisting of 1 gm. of 3-(tricyanovinyl)-indole and 1 gm. Beckacite K (a maleinate resin manufactured by Messrs. Reichhold A.G.) in 20 gm. of benzene. As in the method described in Example I, this solution was poured out on to an aluminum foil and a copy obtained electrophotographically, but with the important difference, that the exposure time for providing a good reproduction of the original is only 30 seconds. In place of Rhodamine-B extra, Rose Bengal, Rosin, Uranine, or Acridine Orange can be used as the sensitizer, with good results.

EXAMPLE IIIB Ten mg Rhodamine-B extra (B.A.S.F.) was dissolved in gm. methylene chloride and added to a solution consisting of 1 gm. of 4-tricyanovinyl2,6- dimethylphenol and I gm. Beckacite K 125 in 20 gm. of benzene. A copy was obtained electrophotographically, as with Example IlIA, the exposure time for providing a good reproduction of the original also being 30 seconds.

EXAMPLE IVA The procedure was the same as in Example III, but with the difference that Methylene Blue was used as the sensitizer. A photoconductive layer having very good properties was obtained by applying the solution of 1 gm. 3-(tricyanovinyl)-indole, 1 gm. Beckacite K 125 and mg. Methylene Blue in 30 cm of dimethyl-formamide to an aluminum foil, and then drying. In order to obtain the same quality of image as when no sensitizer was used, the exposure time must be reduced to 25 percent.

EXAMPLE IVB A photoconductive layer having very good properties was obtained by applying the solution of 1 gm. 4- tricyanovinyl-2,6-dimethyl-phenol, 1 gm. Beckacite K I25 and 15 mg. Methylene Blue in 30 cm of methylene chloride to an aluminum foil, and then drying. Once again, to obtain the same quality of image as in the case when no sensitizer is used, the exposure time had to be reduced to 25 percent.

Examples III and IV illustrate the effect of sensitizers. Their effect is still more clearly shown if sensitization is carried out with sensitizers for infra-red radiation and an iodine-vapor lamp is used to make the exposure, as will be seen'from the following Examples.

EXAMPLE VA One gm. 3-(tricyanovinyl)-N-ethyl-indole and 1 gm. Beckacite K 125 were dissolved in gm. methylene chloride. To this was added 24 mg. crystal-violet BPC in 10 gm. methylene chloride. After application to an aluminum foil, drying and negative charging, exposure was carried out using a 1000 W. quartz-iodine lamp (General Electric) at a distance of 3.5 meters. For an unsensitized plate, the exposure time was 35 seconds, and for the plate sensitized with Crystal-Violet, only 2 seconds. Sensitizers such as xenocyanine, pinacyanol and Bromophenol Blue result in an appreciable shortening of the exposure time required.

EXAMPLE VB One gm. 4-tricyanovinyl-N,N-dimethyl-aniline and 1 gm. Beckacite K 125 were dissolved in 20 gm.

methylene chloride. To this was added 24 mg Crystal- Violet BPC in 10 gm. methylene chloride.

After application to an aluminum foil, drying and negative charging, results were produced which were the same as in Example VA.

EXAMPLE VI One gm. 2-(tricyanovinyl)-pyrrole and 1 gm. of a hydrogenated natural resin, e.g. Hercules Staybelite, produced by the Hercules Powder Company, of Wilmington, U.S.A., were dissolved in 30 gm. methylene chloride. This solution was applied to Cellophane and dried. After the material had been electrically charged by means of a corona discharge, it was laid with the sensitive layer on a book-page printed on both sides and to the back of which was applied a black paper. The material was then exposed for 30 seconds, using a IOO-tungsten lamp at a distance of 50 cm. The exposure thus took place through the Cellophane. After exposure, the image was rendered visible by dusting with a carbon black-pigmented resin powder. A very high contrast positive mirror-image copy resulted.

To obtain a legible positive print, a sheet of paper was laid on to the powder image, after which the powder was transferred from the cellophane to the paper under ,the action of an electrical field.

EXAMPLE VII A photoconductive insulating layer consisting of a solution of 1 gm. 3-(tricyanovinyl)-indole, 1 gm. Beckacite K and 5 mg. chloranil in a mixture of 5 ml. dimethyl-formamide and 15 ml. benzene was applied to an aluminum plate.

The photoconductive insulating layer was charged, exposed in contact with a high-pressure mercury-vapor lamp as the light source, and developed. The exposure time was 5 seconds. Without adding chloranil, a comparable print was obtained after an exposure time of 45 seconds.

EXAMPLE VIII A photoconductive insulating layer consisting of a solution of 1 gm. 4-tricyanovinyl-2,6-dimethyl-phenol, 1 gm. Beckacite K 125 and 7 mg. chloranil in a mixture of IO ml methylene chloride and 10 ml benzene was applied to an aluminum plate. The photoconductive insulating layer was charged, exposed in contact with a high-pressure mercury-vapor lamp as the light source, and developed. The exposure time was 1.5 seconds. Without adding chloranil a comparable print was obtained after an exposure time of 10 seconds.

We claim:

1. A material for electrophotographic reproduction comprising a substrate and a photoconductive insulating layer adhering thereto, the photoconductive insulating layer comprising a resin and a photoconductive substance comprising at least one compound having the general formula:

wherein A represents a radical selected from the group consisting of phenyl, 4-hydroxyphenyl, 4-aminophenyl, 2-pyrryl and 3-indolyl, and R is selected from the group consisting of H and alkyl of l to 5 carbonatoms occupying a nuclear position of A.

2. A material for electrophotographic reproduction as claimed in claim 1, wherein the H-atom linked to the nitrogen atom of the pyrrole or indole nucleus is substituted by an alkyl group having from one to five carbon atoms inclusive.

3. A material for electrophotographic reproduction as claimed in claim 1, wherein the alkyl group is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tertiary butyl.

4. A material for electrophotographic reproduction as claimed in claim 1, wherein the amino group is substituted by an alkyl group having from one to five carbon atoms inclusive.

5. A material for electrophotographic reproduction as claimed in claim 1, wherein the photoconductive substance is 3-(tricyanovinyl)-indole or an N-alkyl substituted derivative thereof.

6. A material for electrophotographic reproduction as claimed in claim 1, wherein the photoconductive substance is Z-(tricyanovinyl)-N-pyrrole or an N-alkyl substituted derivative thereof. I

7. A material for electrophotographic reproduction as claimed in claim 1, wherein the photoconductive substance is 4-tricyanovinyl-2,6-dimethyl phenol.

8. A material for electrophotographic reproduction as claimed in claim 1, where the photoconductive substance is 4-tricyanovinyl-N,N-dimethylor diethylaniline.

9. A material for electrophotographic reproduction as claimed in claim 10, wherein the sensitizer is a phenol sulphone phthalein.

12. A material for electrophotographic reproduction as claimed in claim 10, wherein the optical sensitizer is present in a quantity of up to 3 percent based on the weight of the photoconductive layer.

13. A material for electrophotographic reproduction as claimed in claim 1, wherein the coating weight of the photoconductive insulating layer lies between 1 and 50 grams per square meter of the surface of the substrate.

14. A material for electrophotographic reproduction as claimed in claim 1, wherein the substrate is an aluminum foil.

15. A photoconductive composition comprising a resin and a photoconductive substance comprising at least one compound having the general formula:

wherein A represents a radical selected from the group consistin of hen 1,4-h drox hen 1,4-amino hen l, 2-pyrryl 5nd -ind( )lyl, ari d R is elecl ed from th grol ip 

2. A material for electrophotographic reproduction as claimed in claim 1, wherein the H-atom linked to the nitrogen atom of the pyrrole or indole nucleus is substituted by an alkyl group having from one to five carbon atoms inclusive.
 3. A material for electrophotographic reproduction as claimed in claim 1, wherein the alkyl group is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tertiary butyl.
 4. A material for electrophotographic reproduction as clAimed in claim 1, wherein the amino group is substituted by an alkyl group having from one to five carbon atoms inclusive.
 5. A material for electrophotographic reproduction as claimed in claim 1, wherein the photoconductive substance is 3-(tricyanovinyl)-indole or an N-alkyl substituted derivative thereof.
 6. A material for electrophotographic reproduction as claimed in claim 1, wherein the photoconductive substance is 2-(tricyanovinyl)-N-pyrrole or an N-alkyl substituted derivative thereof.
 7. A material for electrophotographic reproduction as claimed in claim 1, wherein the photoconductive substance is 4-tricyanovinyl-2,6-dimethyl phenol.
 8. A material for electrophotographic reproduction as claimed in claim 1, where the photoconductive substance is 4-tricyanovinyl-N,N-dimethyl- or diethyl-aniline.
 9. A material for electrophotographic reproduction as claimed in claim 1, wherein the ratio by weight of the tricyanovinyl compound to the resin binder is within the range 10:1 to 1:10.
 10. A material for electrophotographic reproduction as claimed in claim 1, wherein the photoconductive layer includes an optical sensitizer.
 11. A material for electrophotographic reproduction as claimed in claim 10, wherein the sensitizer is a phenol sulphone phthalein.
 12. A material for electrophotographic reproduction as claimed in claim 10, wherein the optical sensitizer is present in a quantity of up to 3 percent based on the weight of the photoconductive layer.
 13. A material for electrophotographic reproduction as claimed in claim 1, wherein the coating weight of the photoconductive insulating layer lies between 1 and 50 grams per square meter of the surface of the substrate.
 14. A material for electrophotographic reproduction as claimed in claim 1, wherein the substrate is an aluminum foil.
 15. A photoconductive composition comprising a resin and a photoconductive substance comprising at least one compound having the general formula: wherein A represents a radical selected from the group consisting of phenyl, 4-hydroxyphenyl, 4-aminophenyl, 2-pyrryl and 3-indolyl, and R is selected from the group consisting of H and alkyl of one to five carbon atoms occupying a nuclear position of A. 